1. Field of the Invention
The present invention relates to an image processing technology of reducing color blur included in a color image obtained by image capturing.
2. Description of the Related Art
An image pickup system that produces a color image by image capturing undesirably sometimes generates a color blur, which is an originally nonexistent color, around a bright region in the color image due to chromatic aberration of an imaging optical system (image capturing optical system). Such a color blur is likely to foe generated at wavelengths away from a central wavelength of the imaging optical system. For example, a visible-light image pickup system generates a blue artifact, a red artifact or a purple artifact that is a mixture of the red and blue artifacts in a blurred manner, which are each called a color blur or a purple fringe.
The chromatic aberration can be optically reduced to some extent with a combination of a plurality of lenses having mutually different, dispersions. However, increase of resolution of an image sensor and reduction of size of the imaging optical system in an image pickup apparatus, such as a digital camera, makes it difficult, to optically achieve a sufficient reduction in the chromatic aberration. Thus, reduction in these color blurs is required to be achieved by image processing.
Japanese Patent Laid-open Nos. 2008-147980 and 2008-147981 each disclose an image processing method of estimating an amount of a color blur of each of color components included in an input color image and of subtracting the estimated amounts of the color-blurs from the original color image to reduce the color blurs of the respective color components. Japanese Patent Laid-open Nos. 2008-147980 and 2008-147981 each also disclose a technique of correcting the estimated amounts of the color blurs to avoid excessive subtraction of the color blurs from the color image.
However, in a case of reducing the color blur including multiple color components by the method disclosed in Japanese Patent Laid-open Nos. 2008-147980 and 2008-147981, performing the subtractions of the estimated amounts of the color blurs of the respective color component in a random order (that is, without considering an order of the color components) may cause inversion of a hue and thereby may generate an unnatural color in an image region having a reduced color blur. In other words, a desirable color blur reduction effect may be not achieved.